Oxide semiconductor substrate and schottky barrier diode

ABSTRACT

A schottky barrier diode element having a silicon (Si) substrate, an oxide semiconductor layer and a schottky electrode layer, wherein the oxide semiconductor layer includes a polycrystalline and/or amorphous oxide semiconductor having a band gap of 3.0 eV or more and 5.6 eV or less.

TECHNICAL FIELD

The invention relates to a schottky diode element, an electric circuit,an electric apparatus, an electronic apparatus and a vehicle includingthe same. Further, the invention relates to a structural body, an oxidesemiconductor substrate formed of the structural body, a powersemiconductor device, a diode device and a schottky barrier diodeelement including the same, an electric circuit, an electric apparatus,an electronic apparatus and a vehicle including the same.

BACKGROUND ART

A schottky barrier diode is a diode having rectification functionutilizing an electron barrier formed in the interface of a metal and asemiconductor. As the semiconductor, Si is most commonly used (PatentDocument 1, for example). Further, as a compound semiconductor having aband gap larger than that of Si, GaAs or, recently, SiC has been used(Patent Documents 2 and 3, for example).

A Si-based schottky diode is used in a high-speed switching element, atransmission/receiving mixer in a several GHz frequency band, or afrequency conversion device or the like. A GaAs-based schottky dioderealizes a further higher-speed switching device, and is used in aconverter, a mixer or the like for microwaves. Utilizing a wide bandgap, SiC is expected to be used in an electric car, railroad, powertransmission or the like in which a higher voltage is applied.

A schottky barrier diode is generally used due to its relatively lowcost. However, since it has a small band gap of 1.1 eV, it is requiredto increase the size of the element in order to allow it to have awithstand voltage. The band gap of GaAs is 1.4 eV that is larger thanthat of Si and the withstand voltage of GaAs is superior to that of Si.However, epitaxial growth thereof on a Si substrate is difficult, andhence, it was difficult to obtain crystals suffering less dislocation.SiC has a wide band gap of 3.3 eV, and has a high dielectric breakdownfield, and hence it is a material of which the performance is expectedamong other semiconductors. However, since both production of asubstrate and epitaxial growth require high-temperature processes, useof SiC has problems in respect of mass productivity and cost.

RELATED ART DOCUMENTS Patent Documents

-   Patent Document 1: JP-A-2009-164237-   Patent Document 2: JP-A-H5-36975-   Patent Document 3: JP-A-H8-97441

SUMMARY OF INVENTION

The invention has been attained in view of the above-mentioned problems,and is aimed at providing a schottky barrier diode element havingexcellent current-voltage characteristics by forming, on a Si substrate,a compound semiconductor having a wide band gap at a low cost and by amethod realizing excellent mass productivity.

The invention is aimed at providing an oxide semiconductor substratethat is preferable for use in a schottky barrier diode element, a diodeelement and a power semiconductor element.

According to the invention, the following schottky barrier diode elementor the like are provided.

1. A schottky barrier diode element having a silicon (Si) substrate, anoxide semiconductor layer and a schottky electrode layer, wherein theoxide semiconductor layer comprises a polycrystalline and/or amorphousoxide semiconductor having a band gap of 3.0 eV or more and 5.6 eV orless.2. The schottky barrier diode element according to 1, wherein the oxidesemiconductor comprises one or more selected from the group consistingof In, Ti, Zn, Ga and Sn.3. The schottky barrier diode element according to 1 or 2, wherein theoxide semiconductor layer comprises indium (In) as a main component.4. The schottky barrier diode element according to any one of 1 to 3,wherein the atomic composition percentage of indium relative to thetotal metal elements contained in the oxide semiconductor layer([In]/([In]+[total metal elements other than In])×100) is 30 to 100 atm%.5. The schottky barrier diode element according to any one of 1 to 4,wherein the oxide semiconductor layer is formed on the silicon substrateand the schottky electrode layer is formed on the oxide semiconductorlayer.6. The schottky barrier diode element according to any one of 1 to 4,wherein the schottky electrode layer is formed on the silicon substrateand the oxide semiconductor layer is formed on the schottky electrodelayer.7. The schottky barrier diode element according to any one of 2 to 6,wherein the oxide semiconductor layer further comprises one or moreelements selected from Al, Si, Zn, Ga, Hf, Zr, Ce, Sm and Sn.8. The schottky barrier diode element according to any one of 1 to 7,wherein the carrier concentration at room temperature of the oxidesemiconductor layer is 1×10¹⁴ cm⁻³ or more and 1×10¹⁷ cm³ or less.9. The schottky barrier diode element according to any one of 1 to 8,wherein an edge part of the oxide semiconductor layer is covered by aninsulating film so as not to be exposed.10. An electric circuit comprising the schottky barrier diode elementaccording to any one of 1 to 9.11. An electric apparatus comprising the schottky barrier diode elementaccording to any one of 1 to 9.12. An electronic apparatus comprising the schottky barrier diodeelement according to any one of 1 to 9.13. A vehicle comprising the schottky barrier diode element according toany one of 1 to 9.14. A structural body comprising an oxide semiconductor layer and ametal thin film, wherein

the oxide semiconductor layer comprises polycrystalline and/or amorphousoxide semiconductor having a band gap of 3.0 eV or more and 5.6 eV orless; and

the structural body comprises a region where the oxide semiconductorlayer electrically contacts the metal thin film.

15. The structural body according to 14, wherein the oxide semiconductorcomprises In as a main component.

16. The structural body according to 14 or 15, wherein the metal thinfilm has a work function of 4.7 eV or more.

17. The structural body according to any one of 14 to 16, wherein theoxide semiconductor is crystalline, and

at least one element selected from Al, Si, Ce, Ga, Hf, Zr and Sm iscontained in an amount ratio of 3 at % or more and 30 at % or lessrelative to the total metal elements.

18. The structural body according to any one of 14 to 17, wherein theoxide semiconductor has a carrier concentration at room temperature of1×10¹⁴ cm⁻³ or more and 1×10¹⁷ cm⁻³ or less.

19. The structural body according to any one of 14 to 18, wherein thefilm thickness of the oxide semiconductor layer is 50 nm to 20 μm.

20. An oxide semiconductor substrate in which the structural bodyaccording to any one of 14 to 19 is stacked on a conductive substrate.

21. The oxide semiconductor substrate according to 20, wherein theconductive substrate is composed of one or more selected frommonocrystalline silicone, polycrystalline silicon and microcrystalsilicon.

22. An oxide semiconductor substrate in which the structural bodyaccording to any one of 14 to 19 is stacked on an electricallyinsulating substrate.

23. A power semiconductor element in which the oxide semiconductorsubstrate according to any one of 20 to 22 is used.

24. A diode element in which the oxide semiconductor substrate accordingto any one of 20 to 22 is used.

25. A schottky barrier diode element in which the oxide semiconductorsubstrate according to any one of 20 to 22 is used.

26. The schottky barrier diode element according to 25, wherein themetal thin film serves as a schottky electrode layer.

27. An electric circuit comprising the power semiconductor elementaccording to 23, the diode element according to 24 or the schottkybarrier diode element according to 25 or 26.

28. An electric apparatus comprising the electric circuit according to27.

29. An electronic apparatus comprising the electric circuit according to27.

30. A vehicle comprising the electric circuit according to 27.

According to the invention, it is possible to provide a schottky barrierdiode element having excellent current-voltage characteristics byforming on a Si substrate a compound semiconductor having a wide bandgap at a low cost and by a method that is excellent in massproductivity.

Further, according to the invention, it is possible to provide an oxidesemiconductor substrate that is preferable for use in a schottky barrierdiode element, a diode element and a power semiconductor element.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view schematically showing one embodiment ofthe schottky barrier diode element of the invention;

FIG. 2 is a cross-sectional view schematically showing one embodiment ofthe schottky barrier diode element of the invention; and

FIG. 3 is a cross-sectional view schematically showing one embodiment ofthe schottky barrier diode element of the invention.

MODE FOR CARRYING OUT THE INVENTION 1. Schottky Barrier Diode Element

The schottky barrier diode element of the invention is a schottkybarrier diode element having a silicon (Si) substrate, an oxidesemiconductor layer and a schottky electrode layer, wherein the oxidesemiconductor layer comprises a polycrystalline and/or amorphous oxidesemiconductor having a band gap of 3.0 eV or more and 5.6 eV or less. Byusing a polycrystalline and/or amorphous oxide semiconductor having awide band gap, it is possible to provide a schottky barrier diodeelement having excellent current-voltage characteristics, in particular,a high dielectric breakdown field.

In addition, by using a material having a wide band gap, it becomespossible to use a polycrystalline and/or amorphous material instead of amonocrystal that requires a high production cost in connection withcrystal growth or the like.

The band gap of the oxide semiconductor contained in the oxidesemiconductor layer is preferably 3.1 eV or more and 5.4 eV or less. Byusing an oxide semiconductor having a band gap within this range, it ispossible to provide a schottky barrier diode element having excellentcurrent-voltage characteristics, in particular, a high dielectricbreakdown field.

As an oxide semiconductor having a band gap of 3.0 eV or more and 5.6 eVor less, an oxide containing one or more selected from the groupconsisting of In, Ti, Zn, Ga and Sn can be given. For example, In₂O₃,TiO₂, ZnO, Ga₂O₃, SnO or the like can be given.

It is preferred that the oxide semiconductor contained in the oxidesemiconductor layer be one or more selected from the group consisting ofIn₂O₃, TiO₂, ZnO, Ga₂O₃ and SnO. For example, one obtained by solidsolution of Ti, Zn, Ga or Sn in In₂O₃, a composite oxide of In and Ti,Zn, Ga or Sn or an amorphous oxide containing these elements at aprescribed atomic ratio are included. Further, conductivity of the oxidesemiconductor may be adjusted by appropriately doping with impurities.For example, in respect of performance (sintering density, transversestrength, etc.), it is preferred that the oxide semiconductor compriseIn₂O₃ as a main component.

These oxide semiconductors may be polycrystalline, amorphous or may be amixture of a polycrystalline oxide and an amorphous oxide.

The band gap can be calculated by the following method. That is, on atransparent substrate such as a glass substrate, a 300 nm-thick oxidesemiconductor thin film is formed by sputtering. Then, by means of aUV-VIS spectrophotometer (UV-3100, manufactured by Shimadzu Corporation,for example), transmittance within a range of 250 nm to 1000 nm ismeasured. Subsequently, for the obtained transmittance, hv [eV] isplotted on the x-axis and (αhv)^(1/2)[(eV^(1/2))(cm^(−1/2))] is plottedon the y-axis (Tauc plot).

Here, h is a Planck coefficient [J·s], v is a frequency [s⁻¹], and a isan absorption coefficient [cm⁻¹]. Subsequently, by extrapolating thelinear part to the x-axis to obtain an intersection, a band gap of theoxide semiconductor thin film can be obtained.

When an oxide thin film is present on a colored substrate or in a diodesubstrate, calculation can be conducted similarly by evaluating thespectrum of reflectance after the film surface is exposed.

It is preferred that the oxide semiconductor layer comprise indium (In)as a main component.

The “oxide semiconductor layer comprises indium (In) as a maincomponent” as referred to herein means that the atomic percentage ofindium to total metal elements contained in the oxide semiconductorlayer ([In]/([In]+[total metal elements other than In])×100) be 30 to100 atm %. By using a material based on indium oxide having a large bandgap, it is possible to provide a schottky barrier diode element havingexcellent current-voltage characteristics, in particular, a highdielectric breakdown field.

The amount ratio of indium in the oxide semiconductor layer can beadjusted by changing the amount ratio of indium in a sputtering target,for example. The same can be applied to other elements.

It is preferred that the amount of indium contained in the oxidesemiconductor layer be 30 atm % or more relative to the total metalelements contained in the oxide semiconductor layer. With this amountrange, high withstand voltage and conductivity can be attained at thesame time.

The composition ratio of the elements contained in the oxidesemiconductor layer can be obtained by a quantitative analysis usingsecondary ion mass spectrometry (SIMS). Specifically, after exposing thecross section of the semiconductor layer by a method such as polishing,a quantitative analysis is conducted by a calibration curve method byusing a standard sample of which the concentration is known.

When a film is formed by a sputtering method, the elemental compositionratio of the oxide semiconductor layer is almost equal to the elementalcomposition ratio of a sputtering target.

The elemental compositional ratio of a sputtering target is obtained bya quantitative analysis by means of an inductively coupled plasma massspectrometry (ICP-AES) apparatus. Specifically, the quantity of a samplesolution obtained by dissolving a sputtering target with an acidtreatment is determined by a calibration method by using a standardsample having a known concentration. By converting the concentration ofthe resulting solution into an atomic percentage of the target, theelemental composition ratio of the target can be obtained.

The oxide semiconductor layer may further contain one or more elementsselected from Al, Si, Zn, Ga, Hf, Zr, Ce, Sm and Sn. That is, the oxidesemiconductor layer is composed of indium oxide (In₂O₃) and, optionally,an oxide of an added element. No specific restrictions are imposed on anoxide of the added element.

The added element is preferably one or more elements selected from Al,Si, Zn, Ga, Hf, Ce, Sm and Sn.

The oxide semiconductor layer is not necessarily monocrystalline. It maybe amorphous or polycrystalline.

However, in order to allow the oxide semiconductor layer to exhibitexcellent diode characteristics, the carrier concentration thereof atroom temperature (298K) is preferably 1×10¹⁴ cm⁻³ or more and 1×10¹⁷cm⁻³ or less. If the carrier concentration is less than 1×10¹⁴ cm⁻³, theon-resistance becomes too high, and as a result, undesirable heatgeneration may occur at the time of operation. If the carrierconcentration exceeds 1×10¹⁷ cm⁻³, the resistance becomes too low, andleakage current at the time of applying a reverse bias voltage mayincrease.

The carrier concentration is more preferably 1×10¹⁵ cm⁻³ or more and5×10¹⁶ cm⁻³ or less.

The carrier concentration is measured by the method described in theExamples.

The preferable concentration of the added element other than indiumdiffers by the application of the oxide semiconductor layer; i.e. itdiffers between a case when the layer is used as a crystallinesemiconductor and a case when the layer is used as an amorphoussemiconductor. In the case of a crystal semiconductor, relative tocrystals of indium oxide, Al, Si, Ga, Hf, Zr, Ce and Sm is 3 at % ormore and 30 at % or less relative to total metal elements containing Inand Zn is 5 at % or more and 40 at % or less relative to total metalelements containing In. In addition, Sn is effective to lower theresistance of the target, and is preferably contained in an amount of500 ppm or more and 3 at % or less relative to the total metal elementscontaining In. Sn serves as a donor for crystalline indium oxide andhence it is preferred that the amount thereof not exceed 3 at %.

In the case of an amorphous semiconductor, as a conventionally knowncomposition, a three-component system such as IGZO111, ITZO, IZZrO,IZAlO or the like and a two-component system such as IGO, IZO, ITO orthe like can be used. In this case, the concentration of In is less than90%, the annealing temperature is preferably suppressed to 300° C. orless.

In this case, it is preferred that the carrier concentration be adjustedsuch that it is within a range of 1×10¹⁴ cm⁻³ or more and 1×10¹⁷ cm⁻³ orless by annealing in an oxidizing atmosphere.

As for a silicon (Si) substrate, either an n-type silicon substrate or ap-type silicon substrate can be used. As for the silicon substrate, aconventionally known substrate having excellent surface smoothness suchas a silicon monocrystal substrate, a silicon polycrystalline substrateand a silicon fine crystal substrate can be used.

One morphology of a polycrystal is a fine crystal. A polycrystal is anassembly of monocrystals, and has a clear grain boundary that oftenaffects electric characteristics. Among polycrystals, a fine crystal hasa grain size of on the level of submicron or less, and does not have aclear grain boundary. Therefore, it has an advantage that variations inelectric characteristics by grain boundary scattering are small.

In a schottky electrode layer, a material having a work function of 4.7eV or more is preferably used. Specifically, Ru, Au, Pd, Ni, Ir, Pt oralloys thereof are used. If the work function is below 4.7 eV, theschottky barrier height is short, whereby the amount of leakage at thetime of applying a reverse bias voltage may become large.

Although varied depending on the concentration of impurities of siliconwafer, the work function of a metal used in an ohmic electrode layer ispreferably about 4.1 eV. Taking the adhesiveness into consideration, Tior Mo is preferable.

The measurement of work function can be conducted by a method mentionedlater.

In one embodiment of the schottky barrier diode element of theinvention, an oxide semiconductor layer is formed on a siliconsubstrate, and a schottky electrode layer is formed on the oxidesemiconductor layer.

When n-type silicon wafer is used, an oxide semiconductor layer isstacked on the surface of the substrate, and on the oxide semiconductorlayer, an electrode layer (Pt, Au, Pd, Ni or the like) forming theschottky is arranged. On the backside of the substrate, an electrodelayer (e.g. Ti) that forms ohmic contact with n-type silicon is stacked.In order to ensure conduction, on the backside of the substrate, it ispreferable to stack a good conductor such as Au with Ni being disposed.Ni has effects of preventing diffusion of Au.

In another embodiment of the schottky barrier diode element of theinvention, a schottky electrode layer is formed on the siliconsubstrate, and on the schottky electrode layer, an oxide semiconductorlayer is formed.

When p-type silicon wafer is used, on the surface of the substrate, aschottky electrode layer such as Pt, Au, Pd and Ni is stacked. On theschottky electrode layer, an oxide semiconductor layer is formed by asputtering method. In this case, a schottky barrier is formed in theinterface between a metal such as Pt, Au, Pd and Ni and the oxidesemiconductor layer. Further, by subjecting the surface of the schottkyelectrode layer to an acidification treatment by oxygen plasma or UVozone before forming the oxide semiconductor layer, more excellent diodecharacteristics can be obtained.

Subsequently, on the oxide semiconductor layer, a metal that forms ohmiccontact with the oxide semiconductor (e.g. Ti) is stacked. In this case,as mentioned above, a good conductor such as Au may be further stackedwith Ni being disposed. On the other hand, on the backside of the p-typesilicon wafer, an electrode having good adhesiveness is stacked in orderto assist conductance.

The schottky barrier diode element of the invention may have aconventionally known guard ring structure. A guard ring is stackedbetween the oxide semiconductor layer and the schottky electrode layer,and has an effect of improving withstand voltage. At an end part (edgepart) of the oxide semiconductor layer, an electrical field tends tooccur to cause dielectric breakdown. Therefore, by stacking aninsulating film such as SiO₂ so as to cover this end part, withstandvoltage (dielectric breakdown voltage) can be further increased.

It is preferred that the schottky barrier diode element of the inventionbe covered by an insulating film such that the edge part of the oxidesemiconductor layer is not exposed.

The oxide semiconductor layer, the schottky electrode layer, the ohmicelectrode layer or the like that constitute the schottky barrier diodeelement of the invention can be formed by a conventionally knownsputtering film forming method that is low in cost and has excellentmass productivity, as described in the Examples.

The film thickness of the oxide semiconductor layer is the same as thatof the oxide semiconductor layer in the structural body of theinvention, as described below.

In the interface between the electrode layer and the oxide semiconductorlayer forming the schottky electrode, oxygen is introduced during theschottky electrode sputtering process to conduct reactive sputtering,whereby a thin oxide film having a thickness of 10 nm or less may bestacked.

After forming the oxide semiconductor layer, the layer may be subjectedto an annealing process to crystallize the oxide semiconductor. Bycrystallizing the oxide semiconductor, the on-resistance can bedecreased. No specific restrictions are imposed on the annealingprocess. However, for example, after forming the oxide semiconductorlayer, a treatment is conducted at 300° C. for 2 hours in the air tostabilize the oxidized state. Then, after forming an electrode layer, atreatment is conducted at 200° C. for 1 hour in the air. Thecrystallization can be confirmed by X-ray diffraction (XRD) measurement.

The schottky barrier diode element of the invention has a highdielectric breakdown field. The dielectric breakdown field of theschottky barrier diode of the invention is preferably 0.5 MV/cm or more,more preferably 0.7 MV/cm or more. By this dielectric breakdown field,the diode can be designed into a thin diode. As a result, the size ofthe element can be reduced, whereby heat dissipation can be conductedadvantageously. The n value of the schottky barrier diode of theinvention is preferably 2 or less, more preferably 1.5 or less. By thisn value, the on-resistance is reduced, and as a result, heat generationcan be suppressed.

The dielectric breakdown field and the n value are measured by themethod described in the Examples.

The schottky barrier diode element of the invention can preferably beused in an electric circuit, an electric apparatus, an electronicapparatus, a vehicle and a motor vehicle.

2. Structural Body and Oxide Semiconductor Substrate

The structural body of the invention comprises an oxide semiconductorlayer and a metal thin film, and comprises a region where the oxidesemiconductor layer and the metal thin film electrically contact. Theoxide semiconductor layer comprises polycrystalline and/or amorphousoxide semiconductor having a band gap of 3.0 eV or more and 5.6 eV orless.

The “oxide semiconductor layer and the metal film electrically contact”means that the metal thin film and the oxide semiconductor layer form ajunction, and means a state in which electrons can be freely diffusedfrom the oxide semiconductor to the metal thin film such that the Fermienergies of the both coincident with each other. As for the “regionwhere the oxide semiconductor layer and the metal thin film electricallycontact”, a region where the metal thin film and the oxide semiconductorlayer are directly contacted without interposition of an insulating filmcan be given.

It is preferred that the metal thin film have a work function of 4.7 eVor more.

As the metal thin film having a work function of 4.7 eV or more, a metalsuch as Au, Cr, Cu, Fe, Ir, Mo, Nb, Ni, Pd, Pt, Re, Ru and W and a metaloxide such as In₂O₃, ITO and IZO can be given. In respect of obtainingclear rectification properties, it is advantageous to use a metal havinga larger work function and having a high carrier concentration. A morepreferable range of the work function is 4.8 eV or more, furtherpreferably 5.0 eV or more. Although no specific restrictions are imposedon the upper limit, the upper limit is preferably 5.6 eV or less.

When a metal oxide is used as a metal thin film, it is preferred thatthe carrier concentration be 10²⁰ cm⁻³ or more. If the carrierconcentration is smaller than this range, when stacking on the metalfilm an oxide semiconductor comprising In as a main component, thedegree of spreading of an depletion layer is increased, whereby anincrease in internal resistance occurs or high-speed switchingproperties are adversely affected. Therefore, as a material for a metalthin film stacked on the oxide semiconductor comprising In as a maincomponent, Au, Ir, Ni, Pd or W is more preferable.

In order to increase processability, a slight amount of a metal may beadded in such an amount that does not lower the work function. Forexample, when the material of the metal thin film is Au, an alloy formedby adding Ag and Cu can be used. If the material of the metal thin filmis Pd, an alloy formed of adding Ag and Cu can be used.

The work function is measured by means of a photoelectron spectrometer(AC-3 manufactured by Riken Keiki Co., Ltd., for example). The workfunction varies depending on a surface treatment with an acid, an alkalior the like or a UV washing or the like. The work function as referredto herein means a value that is obtained by a measurement withoutconducting a treatment after film formation.

It is preferred that the above-mentioned oxide semiconductor comprise Inas a main component. The “comprises In as a main component” as referredto herein is as explained above with reference to the schottky barrierdiode element of the invention. As for the band gap, the same asmentioned above with reference to the schttoky barrier diode element ofthe invention can be applied.

The above-mentioned oxide semiconductors may be polycrystalline,amorphous, or may be a mixture of polycrystalline semiconductors andamorphous semiconductors. It is preferred that the oxide semiconductorbe crystalline.

It is preferred that at least one element selected from Al, Si, Ce, Ga,Hf, Zr and Sm be contained in the oxide semiconductor. The contentthereof is preferably 3 at % or more and 30 at % or less relative to thetotal metal elements of the oxide semiconductor.

It is preferred that the oxide semiconductor mentioned above have acarrier concentration of 1×10¹⁴ cm⁻³ or more and 1×10¹⁷ cm⁻³ or less atroom temperature (298K). The carrier concentration is more preferably1×10¹⁵ cm⁻³ or more and 5×10¹⁶ cm⁻³ or less.

A carrier concentration of less than 1×10¹⁴ cm⁻³ is not preferable,since when it is used as a diode elements, the on-resistance isincreased too high, and heat generation may occur during operation. Whenthe carrier concentration exceeds 1×10¹⁷ cm⁻³, the resistance becomestoo low, and leakage current during reverse bias may increase.

As for the thin film forming technology, a CVD method such as a thermalCVD method, a CAT-CVD method, a photo-CVD method, a mist CVD method, anMO-CVD method and a plasma CVD method; a film-forming method with atomiclayer level control such as MBE and ALD; a PVD method such as ionplating, ion beam sputtering and magnetron sputtering; a method in whicha conventionally known ceramic process is used such as a doctor bladingmethod, an injection method, an extrusion method, a heat pressingmethod, a sol-gel method and an aerosol deposition method; and a wetmethod such as a coating method, a spin coating method, a printingmethod, a spray method, an electrodeposition method, a plating method, amicellar electrolysis method can be used.

The dielectric breakdown field of the structural body of the inventionis 0.5 to 3 MV/cm that is significantly superior to a conventionalsilicon-based diode. The required withstand voltage varies according tothe application and the purpose, and 0.2 μm to 1.2 μm is required for a60V withstand voltage, 2 μm to 12 μm is required for a 600V withstandvoltage. In particular, when a film thickness of 2 μm or more isrequired, it is advantageous in respect of productivity process to use aCVD method or a wet method as compared with a PVD method.

The film thickness of the oxide semiconductor is preferably 50 nm ormore and 20 μm or less. If the film thickness is below 50 nm, thewithstand voltage becomes about 10V, that is insufficient as adielectric breakdown voltage in many applications. If the film thicknessexceeds 20 μm, a withstand voltage of 5000V can be realized. However, inthis case, the on-resistance is increased, heat generation may occur atthe time of switching. A more preferable range of the film thickness is200 nm or more and 12 μm or less.

These film thicknesses can be measured by a contact type differentialtransformer such as a surfcoder and DEKTAK or an electron microscopesuch as TEM and SEM.

The structural body of the invention can preferably be used as an oxidesemiconductor substrate by stacking on a conductive substrate or anelectrically insulating substrate.

The oxide semiconductor substrate of the invention has rectificationproperties, and can preferably be used for producing a schottky barrierdiode element, a power semiconductor element and a diode element. Thatis, it is an effective intermediate.

When used as the schottky barrier diode element, in the structural bodyof the invention, the metal thin film functions as the schottkyelectrode layer, the oxide semiconductor layer that electricallycontacts the metal thin film functions as an oxide semiconductor layer.

In the oxide semiconductor substrate of the invention, the structuralbody may be stacked either on the conductive and/or electricallyinsulating substrate. In respect of excellent heat dissipation, use of aconductive substrate is advantageous.

As the conductive substrate, a conventionally known substrate excellentin surface smoothness such as a silicon monocrystal substrate, a siliconpolycrystalline substrate, a silicon fine crystal substrate or the likecan be used.

One form of polycrystal is fine crystal. A polycrystal is an assembly ofmonocrystals, and a clear boundary is present, that often affectselectrical properties. Among them, fine crystals have a grain size of onthe level of submicron or less, and a clear boundary is not present. Forthis reason, it has an advantage that variations in electric propertiesdue to scattering in grain boundary are small.

The properties required for the oxide semiconductor substrate of theinvention are surface smoothness. If used in the vertical direction,conductivity is also required. One that can realize these conditions ata low cost is a silicon substrate, although silicon is not essential. Ametal such as Cu, Al, Mo, W, Ni, Cr, Fe, Nd, Au, Ag, Nd and Pd andalloys thereof can be used. In particular, if a metal material havinghigh thermal conductance is used, effects of heat dissipation can beexpected. According to need, it may have a heat sink structure. Further,a substrate formed of compound monocrystal wafer such as GaAs and InPand various oxides, nitrides, carbides or the like such as Al₂O₃, ZnO,MgO, SrTiO₃, YSZ, lanthanum aluminate, Y₃Al₅O₁₂, NdGaO₃, sapphire, AlN,GaN, SiC, alkaline-free glass and soda lime glass can be used. When usedin lateral direction, the substrate may be insulative.

The vertical direction means that electric current passes in thevertical direction relative to the film surface of the oxidesemiconductor. The lateral direction means that electric current passesin the horizontal direction relative to the film surface of the oxidesemiconductor.

As the electrically insulating substrate, in addition to glass, asubstrate of a resin such as polycarbonate, polyarylate, polyethyleneterephthalate, polyether sulfone, polyimide, a phenol resin or the likecan be used. Since the structural body of the invention does not needprocessing at high temperatures, a power source or the like of a circuitfor driving a display such as a liquid crystal display or an organic ELdisplay and a display can be mounted on the same substrate.

The oxide semiconductor substrate of the invention can preferably beused in each of a power semiconductor element, a diode element and aschottky barrier diode element. An electric circuit that comprises oneor more of the power semiconductor element, the diode element and theschottky barrier diode element is preferably used in each of an electricapparatus, an electronic apparatus and an electric vehicle.

The invention provides a stacked body that is preferable for use as amember constituting a power semiconductor element, specifically, a diodeelement or an IGBT (insulated gate bipolar transistor) element, MOSFET(metal oxide semiconductor field effect transistor). In particular, asfor the diode element, a schottky barrier diode element, a PN diodeelement and a PIN diode element can be preferably provided.

Here, as the type of the diode, a rectification diode used in a powersource circuit, a first recovery diode used in a PWM type invertercircuit or the like, it is possible to suppress heat generation, wherebypower consumption can be decreased. In particular, an inverter circuithas a high operation frequency, and hence, a short recovery time at thetime of switching is required. In this respect, as compared with theconventional first recovery diode, not only it has a small filmthickness, but also it is of unipolar. Therefore, the recovery time canbe significantly shortened. Accordingly, if the operational frequency ishigh, it is possible to take most of the characteristics of the diode ofthe invention.

For the invertor circuit for a vehicle, conventionally, GTO (GateTurn-Off thyristor) had been used. GTO is suited for switching of largepower, the frequency is about 500 Hz. Therefore, noises generated at thetime of moving posed a problem. Therefore, in many of vehicles or EVsthat had become available in recent years, IGBT has been mounted. Theswitching speed of IGBT can be increased to several 10 kHz. As a result,it is possible to suppress generation of noises, and also to reduce thesize of peripheral members.

In principle, IGBT has small switching loss. However, since it has highoperation frequency, reducing the leakage current in reverse directionof a first recovery diode used in combination has great effects onreduction of power consumption. Therefore, the diode of the inventionhaving small leakage current in a reverse direction as compared withconventional Si diodes is particularly effective as a first recoverydiode used in an IGBT inverter. Therefore, when a further smoothoperation is required by increasing the operation frequency,advantageous effects are further increased. Further, since heatgeneration can be suppressed, cooling mechanism can be simplified. Forexample, in the case of EV, it has effects of integrating a plurality ofcooling mechanisms that were conventionally required by means of aradiator of 110° C.

EXAMPLES

Hereinbelow, the Examples of the invention will be explained withreference to the drawings.

Example 1

FIG. 1 is a cross-sectional view schematically showing the schottkybarrier diode element obtained in Example 1.

First, an n-type silicon (Si) substrate 11 having a resistivity of 0.02Ω·cm was prepared. By treating with dilute hydrofluoric acid, anaturally oxidized film formed on the surface of the substrate wasremoved. This Si substrate was mounted in a sputtering apparatus(HSM552, manufactured by Shimadzu Corporation). By using a sintered bodyhaving a composition of In₂O₃:Ga₂O₃=95:5 (wt %) as a sputtering target,sputtering discharge was caused to occur under conditions of RF100 W. Asa result, on the surface of the Si substrate from which the oxidizedfilm had been removed, a 300 nm-thick oxidized film (IGO film) 12containing indium and gallium was formed.

The substrate 11 also functions as a contact electrode.

Subsequently, this IGO film was patterned by photolithography, therebyto form a desired pattern. In the air, annealing was conducted at 300°C. for 2 hours, whereby an IGO film was crystallized. The crystal stateof the IGO film was confirmed by an XRD measurement, and as a result, itwas revealed that the IGO film was polycrystalline.

The Si substrate with this polycrystalline IGO film was again mounted ina sputtering apparatus, and film formation by sputtering was conductedby using a Pt target. As a result, a Pt electrode 13 was formed on thepolycrystalline IGO film, whereby a schottky junction was obtained.

Subsequently, this substrate was again immersed in dilute hydrofluoricacid to remove a naturally oxidized film formed on the backside of thesubstrate on which no polycrystalline IGO film was not formed. Filmswere formed by sputtering in the order of a Ti layer 14, a Ni layer 15and an Au layer 16, whereby an ohmic electrode was formed. Finally, astacked body obtained by forming the ohmic electrode was subjected toannealing in the air at 200° C. for 1 hour, whereby a schottky barrierdiode element 10 was obtained.

In order to confirm the carrier concentration of the IGO film at roomtemperature, CV (capacitance-voltage) measurement was conducted. Thecapacitance C [F/cm²] of a depletion layer per unit area is expressed asC=∈/W. Here, ∈ is the dielectric constant [F/cm] of a semiconductor andW is the width [cm] of a depletion layer. When a forwardly-directed biasvoltage V [V] is applied to the schottky diode, the width of thedepletion layer is W={2∈(φ−V)/qN}(½). Therefore, C={q∈N/2(φ−V)}(½).Here, q is an elementary charge (=1.6×10⁻¹⁹ [C]) and φ is a built-inpotential [V], showing difference in contact difference potentialbetween the Pt electrode and the IGO film.

After obtaining CV measurement results, C⁻²−V characteristics areplotted, and a doping concentration (=carrier concentration) N can beobtained from the gradient. As a result, the following was revealed.That is, the IGO film after forming by sputtering had a low resistanceand the depletion layer was not widened, but after annealing in the airat 300° C. for 2 hours, CV measurement was possible. As a result ofcalculation from the gradient of C⁻²−V, the carrier concentration wasfound to be 5×10¹⁵ cm³.

The current-voltage characteristics of the resulting schottky barrierdiode element were measured to obtain an n-value and a reverse withstandvoltage. Here, the n-value is a parameter showing the characteristics ofthe schottky barrier diode element as shown by the following formula(1). As n becomes closer to 1, ideal device characteristics can beobtained.I=I ₀[exp(eV/nkT)]  (1)I: Density of total currents flowing from the oxidized film towards theSi substrate [A/cm²]e: Charges of electrons 1.60×10⁻¹⁹[C]V: Voltage [V] to be applied to elementI₀: Current density [A/cm²] when the voltage V applied to the element is0V.k: Boltzmann constant 1.38×10⁻²³ [J/K]T: Temperature [K]

As a result, it was found that the n value was 1.3 and the reversewithstand voltage was 20V. This reverse withstand voltage corresponds toa dielectric breakdown field of 0.67 MV/cm, and is twice as high as thatof a conventional schottky barrier diode obtained by usingmonocrystalline Si. The reverse withstand voltage and the dielectricbreakdown field have the following relationship: Reverse withstandvoltage (V)=Dielectric breakdown field (V/cm)×Semiconductor filmthickness (cm)

The results obtained above are shown in Table 1. The “forwardly-directedvoltage” shown in the table means a voltage required for allowingcurrent of 0.1 mA/cm² to pass through the element, and the “on-currentdensity” is a current density when a voltage of 10V is applied to theelement.

Examples 2 to 9

As shown in Table 1, by using a sputtering method, schottky barrierdiode elements were prepared and evaluated in the same manner as inExample 1 while changing the compositions of the schottky electrode andthe semiconductor. The results are shown in Table 1.

Example 10

FIG. 2 is a cross-sectional view showing the schottky barrier diodeelement obtained in Example 10.

First, a p-type silicon substrate 21 having a resistivity of 0.02 Ω·cmwas prepared. A naturally oxidized film was removed by dilutehydrofluoric acid, and film formation was conducted by sputtering byusing a Pd target, whereby a Pd electrode 22 was formed. Subsequently,the surface of this Pd electrode was subjected to an oxidizing treatmentwith UV ozone. Then, in the same manner as in Example 1, an IGO film 23was formed by sputtering. The film was subjected to annealing in the airat 300° C. for 1 hour. Films were formed by sputtering in the order of aTi layer 24, a Ni layer 25 and an Au layer 26, whereby an ohmicelectrode was formed.

For the backside of the p-type silicon substrate (on the surfaceopposite to the surface on which the Pd electrode was formed), afterremoving a naturally oxidized film with dilute hydrofluoric acid, a TiAlfilm 27 was formed by sputtering by using a TiAl alloy as a target.Finally, annealing was conducted in the air at 200° C. for 1 hour,whereby a schottky barrier diode element 20 was obtained. This diode hada polarity reverse to that of the diodes obtained in Examples 1 to 9.When p-type silicon wafer side is connected to plus, current flows inthe forward direction, and when p-type silicon wafer side is connectedto minus, current flows in the reverse direction.

The thus obtained element was evaluated in the same manner as inExample 1. The results are shown in Table 1.

Example 11

FIG. 3 is a cross-sectional view schematically showing the schottkybarrier diode element obtained in Example 11.

In the same manner as in Example 1, an IGO film 32 as an oxidesemiconductor was formed by sputtering on an n-type silicon substrate31. After annealing the film in the air at 300° C. for 1 hour, anegative resist (manufactured by AZ Electronic Material Co., Ltd.) wasapplied by spin coating. By prebaking, exposure, development and postbaking, a ring-like pattern was formed in an edge part of the IGO film.Subsequently, the film was mounted in a sputtering apparatus, and byusing SiO₂ as a target, film formation was conducted by sputtering at RFof 100 W for 50 minutes, whereby a 50 nm-thick SiO₂ film was formed.Subsequently, the film was immersed in a photoresist stripper, and anunnecessary part of the photoresist was peeled off together with the IGOfilm. In this way, a guard ring 37 of the IGO film was formed.Hereinafter, in the same manner as in Example 1, a Pt electrode 33 andan ohmic electrode of Ti34, Ni35 and Au36 were formed, whereby aschottky diode electrode 30 provided with a guard ring was prepared.

The obtained element was evaluated in the same manner as in Example 1.The results are shown in Table 1. Due to the effect of a guard ring, theelement exhibited further excellent withstand voltage properties thanthose obtained in Example 1.

TABLE 1 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Schottky electrode Pt Au PdRu Ni Pt Work function (eV) of 5.6 5.1 5.5 4.7 5.1 5.6 Schottkyelectrode Substrate Si wafer (n type) Si wafer (n type) Si wafer (ntype) Si wafer (n type) Si wafer (n type) Si wafer (n type) Topelectrode Pt Au Pd Ru Ni Pt Contact electrode Si Si Si Si Si Si Ohmicelecrode Ti/Ni/Au Ti/Ni/Au Ti/Ni/Au Ti/Ni/Au Ti/Ni/Au Ti/Ni/Au Workfunction (eV) of ohmic 4.1 4.1 4.1 4.1 4.1 4.1 electrode Semiconductorcomposition (wt %) In₂O₃:Ga₂O₃ = In₂O₃:ZnO = In₂O₃:SiO₂ = In₂O₃:Al₂O₃ =In₂O₃:HfO₂ = In₂O₃:CeO₂ = 95:5 95:5 95:5 95:5 95:5 95:5 Composition ofsemiconductor In:Ga = In:Zn = In:Si = In:Al = In:Hf = In:Ce = (at %)92.8:7.2 91.8:8.2 89.2:10.8 87.5:12.5 96.6:3.4 95.9:4.1 Film thicknessof semiconductor 300 300 300 300 300 300 (nm) Annealing conditions afterIn the air, In the air, In the air, In the air, In the air, In the air,formation of semiconductor film 300° C., 2 h 300° C., 2 h 300° C., 2 h300° C., 2 h 300° C., 2 h 300° C., 2 h Final annealing conditions In theair, In the air, In the air, In the air, In the air, In the air, 200°C., 1 h 200° C., 1 h 200° C., 1 h 200° C., 1 h 200° C., 1 h 200° C., 1 hBand gap (eV) of oxide 3.3 3.2 3.2 3.5 3.6 3.6 semiconductor filmCarrier concentration (cm⁻³) 5 × 10¹⁵ 2 × 10¹⁶ 1 × 10¹⁵ 1 × 10¹⁴ 1 ×10¹⁵ 1 × 10¹⁵ n value 1.3 1.3 1.3 1.3 1.3 1.3 Dielectric breakdown field0.67 0.5 0.7 0.8 0.7 0.67 (MV/cm) Results of XRD PolycrystallinePolycrystalline Polycrystalline Polycrystalline PolycrystallinePolycrystalline measurement of semiconductor Forwardly-directed voltage(V) 0.8 0.9 0.9 0.9 0.9 0.8 On-current density(A/cm²) >10 >10 >10 >10 >10 >10 Ex. 7 Ex. 8 Ex. 9 Ex. 10 Ex. 11 Schottkyelectrode Pt Pt Pt Pd Pt Work function (eV) of 5.6 5.6 5.6 5.5 5.6Schottky electrode Substrate Si wafer (n type) Si wafer (n type) Siwafer (n type) Si wafer (p type) Si wafer (n type) Top electrode Pt PtPt TiAl Pt Contact electrode Si Si Si Si Si Ohmic elecrode Ti/Ni/AuTi/Ni/Au Ti/Ni/Au Ti/Ni/Au Ti/Ni/Au Work function (eV) of ohmic 4.1 4.14.1 5 4.1 electrode Semiconductor composition (wt %) In₂O₃:Sm₂O₃ =In₂O₃:Ga₂O₃:ZnO = In₂O₃:SnO₂:ZnO = In₂O₃:Ga₂O₃ = In₂O₃:Ga₂O₃ = 95:525:35:40 45:20:35 95:5 95:5 Composition of semiconductor In:Sm =In:Ga:Zn = In:Sn:Zn = In:Ga = In:Ga = (at %) 96.0:4.0 17.2:35.7:47.031.8:26.0:42.2 92.8:7.2 92.8:7.2 Film thickness of semiconductor 300 300300 300 300 (nm) Annealing conditions after In the air, In the air, Inthe air, In the air, In the air, formation of semiconductor film 300°C., 2 h 300° C., 2 h 300° C., 2 h 300° C., 2 h 300° C., 2 h Finalannealing conditions In the air, In the air, In the air, In the air, Inthe air, 200° C., 1 h 200° C., 1 h 200° C., 1 h 200° C., 1 h 200° C., 1h Band gap (eV) of oxide 3.5 3.3 3.0 3.3 3.4 semiconductor film Carrierconcentration (cm⁻³) 2 × 10¹⁵ 1 × 10¹⁵ 1 × 10¹⁷ 5 × 10¹⁵ 3 × 10¹⁵ nvalue 1.3 1.3 1.3 1.3 1.2 Dielectric breakdown field 0.67 0.67 0.4 0.670.85 (MV/cm) Results of XRD Polycrystalline Amorphous AmorphousPolycrystalline Polycrystalline measurement of semiconductorForwardly-directed voltage (V) 0.8 1.3 1.3 1.2 1.2 On-current density(A/cm²) >10 >10 >10 >10 >10

Example 12

An n-type silicon (Si) substrate having a resistivity of 0.02 Ω·cm wasprepared. By treating with dilute hydrofluoric acid, a naturallyoxidized film formed on the surface of the substrate was removed. ThisSi substrate was mounted in a sputtering apparatus (HSM552, manufacturedby Shimadzu Corporation). First, Ti was formed as an ohmic electrode.Subsequently, by using a sintered body having a composition ofIn₂O₃:Ga₂O₃=78:22 (wt %) as a sputtering target, sputtering dischargewas conducted at RF of 100 W. As a result, on the Ti layer formed on theSi substrate, a 1 μm-thick oxidized film (IGO film) containing indiumand gallium was formed.

Subsequently, the IGO film was subjected to annealing in the air at 300°C. for 1 hour. Then, patterning was conducted by photolithography toobtain a desired pattern. Then, annealing was conducted in the air at300° C. for 1 hour. As a result of evaluating the IGO film by XRD, nocrystalline peak was observed. It was confirmed that the film wasamorphous.

The substrate provided with this amorphous IGO film was again mounted ina sputtering apparatus. Film formation by sputtering was conducted byusing a Ni target, and a Ni electrode was formed on the amorphous IGOfilm, whereby a schottky barrier junction was obtained. Further, Au wasformed into a film on this Ni electrode by sputtering, whereby aschottky barrier diode element having a simple configuration wasobtained. The resulting element was evaluated in the same manner as inExample 1. The results are shown in Table 2.

Examples 13 to 20

Schottky barrier diode elements were prepared and evaluated in the samemanner as in Example 1 while changing the composition or the like of theoxide semiconductor appropriately. The results are shown in Table 2.

The “4H-SiC” means a hexagonal SiC substrate having a 4-layer repeatingstructure, and the “YSZ” means a yttrium stabilized zirconium substrate.

Further, since high resistant substrates were used in Examples 13, 16,18, 19 and 20, measurement of electricity was conducted by applying aterminal to the ohmic electrode and the schottky electrode.

Comparative Example 1

An n-type silicon (Si) substrate having a resistivity of 0.02 Ω·cm wasprepared. By treating with dilute hydrofluoric acid, a naturallyoxidized film formed on the surface of the substrate was removed. ThisSi substrate was mounted in a sputtering apparatus (HSM552, manufacturedby Shimadzu Corporation). First, Ti was formed as an ohmic electrode.Subsequently, by using a SiC target (manufactured by Sumitomo OsakaCement Co., Ltd.) as a sputtering target, sputtering discharge wasconducted at RF of 100 W. As a result, on the Ti layer formed on the Sisubstrate, a 1 μm-thick SiC film was formed.

Subsequently, the SiC film was patterned by photolithography to obtain adesired pattern. Then, annealing was conducted in the air at 300° C. for1 hour. As a result of evaluating the SiC film by XRD and SEM, the filmwas confirmed to be polycrystalline.

The substrate provided with this polycrystalline SiC film was againmounted in a sputtering apparatus. Film formation by sputtering wasconducted by using a Ni target, and a Ni electrode was formed on thepolycrystalline SiC film, whereby a schottky barrier junction wasobtained. Further, Au was formed into a film on this Ni electrode bysputtering, whereby a schottky barrier diode element having a simpleconfiguration was obtained.

The resulting element was evaluated in the same manner as in Example 1.The results are shown in Table 2.

The element obtained in Comparative Example 1 had a carrierconcentration of 5×10¹⁵ cm⁻³. However, it had an n value exceeding 10,showing no satisfactory diode characteristics. The dielectric breakdownfield was 0.1 MV/cm.

Comparative Example 2

A schottky barrier diode composed of polycrystalline GaN was preparedand evaluated in the same manner as in Comparative Example 1, exceptthat sputtering was conducted by using monocrystalline GaN as a targetinstead of the SiC target. The results obtained are shown in Table 2.

The element obtained in Comparative Example 2 had an n value exceeding10, showing no satisfactory diode characteristics. The dielectricbreakdown field was 0.1 MV/cm.

Comparative Example 3

A schottky barrier diode was prepared and evaluated in the same manneras in Comparative Example 1, except that an oxide material having acomposition of In₂O₃:Al₂O₃=20:80 wt % was used as a target instead ofthe SiC target and the annealing after the semiconductor film formationwas conducted at 150° C. The results are shown in Table 2.

The element obtained in Comparative Example 3 had a sufficiently largeband gap of 5.8 eV or more, but had a significantly small carrierconcentration of less than 10¹³ cm⁻³. Therefore, it was impossible toobtain sufficient forwardly-directed electric current.

TABLE 2 Example 12 Example 13 Example 14 Example 15 Example 16 Example17 Schottky electrode Ni Ni Ni Ni Ni Ni Work function (eV) of Schottky5.1 5.1 5.1 5.1 5.1 5.1 electrode Substrate Si wafer (n type) Sapphire4H—SiC Si wafer (n type) YSZ Polycrystalline Si wafer (n type) Topelectrode Au Au Au Au Au Au Contact electrode Ti Ti Ti Ti Ti Ti Ohmicelectrode Ti Ti Ti Ti Ti Ti Work function (eV) of Ohmic 4.1 4.1 4.1 4.14.1 4.1 electrode Semiconductor composition (wt %) In₂O₃:Ga₂O₃ =In₂O₃:Ga₂O₃ = In₂O₃:Ga₂O₃ = In₂O₃:TiO₂ = In₂O₃:ZnO = In₂O₃:SnO₂ = 78.2285:15 90:10 81:19 72:28 69:31 Semiconductror composition (at %) In:Ga =In:Ga = In:Ga = In:Ga = In:Zn = In:Sn = 70.5:29.5 79.3:20.7 85.9:14.171.0:29.0 60.1:39.9 70.7:29.3 Semiconductor film thickness (μm) 1.0 1.01.0 1.0 1.0 1.0 Annealing conditions after formation In the air, In theair, In the air, In the air, In the air, In the air, of semiconductorfilm 300° C., 1 h 300° C., 1 h 280° C., 1 h 150° C., 1 h 250° C., 1 h250° C., 1 h Final annealing Not conducted Not conducted Not conductedNot conducted Not conducted Not conducted Band gap (eV) of oxide 3.2 3.13.1 3.1 3.2 3.1 semiconductor film Carrier concentration (cm⁻³) 3 × 10¹⁴1 × 10¹⁵ 2 × 10¹⁵ 2 × 10¹⁶ 1 × 10¹⁷ 2 × 10¹⁵ n value 2.2 2.3 2.8 3.5 3.63.1 Dielectric breakdown field (MV/cm) 2.7 2.5 2.3 2.2 2.3 2.2 Resultsof XRD measurement of Amorphous Amorphous Amorphous Amorphous AmorphousAmorphous semiconductor Forwardly-directed voltage (V) 2.5 2.3 2.3 2.12.5 2.4 On-current density(A/cm²) >10    >10    >10    >10    >10    >10    Example 18 Example 19Example 20 Comp. Ex. 1 Comp. Ex. 2 Comp. Ex. 3 Schottky electrode Ni NiNi Ni Ni Ni Work function (eV) of 5.1 5.1 5.1 5.1 5.1 5.1 Schottkyelectrode Substrate Alkali-free glass Alkali-free glass Alkali-freeglass Si wafer Si wafer Si wafer (n type) (n type) (n type) Topelectrode Au Au Au Au Au Au Contact electrode Mo Mo Mo Ti Ti Ti Ohmicelectrode Ti Ti Ti Ti Ti Ti Work function (eV) of Ohmic 4   4   4   4.14.1 4.1 electrode Semiconductor composition In₂O₃:Ga₂O₃:ZnO =In₂O₃:Ga₂O₃:Al₂O₃ = In₂O₃:Ga₂O₃:Al₂O₃ = SiC GaN In₂O₃:Al₂O₃ = (wt %)44.2:29.9:25.9 10:50:40 10:60:30 20:80 Semiconductror compositionIn:Ga:Zn = In:Ga:Al = In:Ga:Al = — — In:Al = (at %) 33.3:33.3:33.35.2:38.4:56.4 5.5:49.2:45.3 8.4:91.6 Semiconductor film thickness 1.01.0 1.0 1.0 1.0 1.0 (μm) Annealing conditions after In the air, In theair, In the air, In the air, In the air, In the air, formation ofsemiconductor 150° C., 1 h 150° C., 1 h 150° C., 1 h 300° C., 1 h 300°C., 1 h 150° C., 1 h film Final annealing Not conducted Not conductedNot conducted Not conducted Not conducted Not conducted Band gap (eV) ofoxide 3.4 5.6 5.4 2.8 2.7 5.8 semiconductor film Carrier concentration(cm⁻³) 2 × 10¹⁵ 2 × 10¹⁴ 9 × 10¹⁴ 5 × 10¹⁵ 5 × 10¹⁵ <1 × 10¹³ n value2.2 2.2 2.2 >10    >10    >10    Dielectric breakdown field 2.3 2.3 2.30.1 0.1 >10    (MV/cm) Results of XRD measurement Amorphous AmorphousAmorphous Polycrystalline Polycrystalline Amorphous of semiconductorForwardly-directed voltage 2.3 2.3 2.3 4   4.5 >10    (V) On-currentdensity (A/cm²) >10    >10    >10    1.2 1   <1 × 10⁻⁴

INDUSTRIAL APPLICABILITY

The schttoky barrier diode element of the invention can be preferablyused in an electric circuit, an electric apparatus, an electronicapparatus, an electric vehicle or the like that require a high-speedoperation or switching properties.

Although only some exemplary embodiments and/or examples of thisinvention have been described in detail above, those skilled in the artwill readily appreciate that many modifications are possible in theexemplary embodiments and/or examples without materially departing fromthe novel teachings and advantages of this invention. Accordingly, allsuch modifications are intended to be included within the scope of thisinvention.

The specification of a Japanese application on the basis of which thepresent application claims Paris Convention priority is incorporatedherein by reference in its entirety.

The invention claimed is:
 1. A schottky barrier diode element having asilicon (Si) substrate, an oxide semiconductor layer and a schottkyelectrode layer, wherein the oxide semiconductor layer comprises apolycrystalline and/or amorphous oxide semiconductor having a band gapof 3.0 eV or more and 5.6 eV or less.
 2. The schottky barrier diodeelement according to claim 1, wherein the oxide semiconductor comprisesone or more selected from the group consisting of In, Ti, Zn, Ga and Sn.3. The schottky barrier diode element according to claim 1, wherein theoxide semiconductor layer comprises indium (In) as a main component. 4.The schottky barrier diode element according to claim 1, wherein theatomic composition percentage of indium relative to the total metalelements contained in the oxide semiconductor layer ([In]/([In]+[totalmetal elements other than In])×100) is 30 to 100 atm %.
 5. The schottkybarrier diode element according to claim 1, wherein the oxidesemiconductor layer is formed on the silicon substrate and the schottkyelectrode layer is formed on the oxide semiconductor layer.
 6. Theschottky barrier diode element according to claim 1, wherein theschottky electrode layer is formed on the silicon substrate and theoxide semiconductor layer is formed on the schottky electrode layer. 7.The schottky barrier diode element according to claim 2, wherein theoxide semiconductor layer further comprises one or more elementsselected from Al, Si, Zn, Ga, Hf, Zr, Ce, Sm and Sn.
 8. The schottkybarrier diode element according to claim 1, wherein the carrierconcentration at room temperature of the oxide semiconductor layer is1×10¹⁴ cm⁻³ or more and 1×10¹⁷ cm⁻³ or less.
 9. The schottky barrierdiode element according to claim 1, wherein an edge part of the oxidesemiconductor layer is covered by an insulating film so as not to beexposed.
 10. An electric circuit comprising the schottky barrier diodeelement according to claim
 1. 11. An electric apparatus comprising theschottky barrier diode element according to claim
 1. 12. An electronicapparatus comprising the schottky barrier diode element according toclaim
 1. 13. A vehicle comprising the schottky barrier diode elementaccording to claim
 1. 14. A structural body comprising an oxidesemiconductor layer and a metal thin film, wherein the oxidesemiconductor layer comprises polycrystalline and/or amorphous oxidesemiconductor having a band gap of 3.0 eV or more and 5.6 eV or less;the oxide semiconductor comprises In as a main component; the oxidesemiconductor is crystalline and comprises at least one element selectedfrom Al, Si, Ce, Ga, Hf, Zr, Sm, Zn and Sn, and if at least one elementselected from Al, Si, Ce, Ga, Hf, Zr and Sm is contained, the contentthereof is 3 at % or more and 30 at % or less relative to the totalmetal elements, if Zn is contained, the content thereof is 5 at % ormore and 40 at % or less relative to the total metal elements, and if Snis contained, the content thereof is 500 ppm at % or more and 3 at % orless relative to the total metal elements; and the structural bodycomprises a region where the oxide semiconductor layer electricallycontacts the metal thin film.
 15. The structural body according to claim14, wherein the metal thin film has a work function of 4.7 eV or more.16. The structural body according to claim 14, wherein the oxidesemiconductor has a carrier concentration at room temperature of 1×10¹⁴cm⁻³ or more and 1×10¹⁷ cm⁻³ or less.
 17. The structural body accordingto claim 14, wherein the film thickness of the oxide semiconductor layeris 50 nm to 20 μm.
 18. An oxide semiconductor substrate in which thestructural body according to claim 14 is stacked on a conductivesubstrate.
 19. The oxide semiconductor substrate according to claim 18,wherein the conductive substrate is composed of one or more selectedfrom monocrystalline silicone, polycrystalline silicon and microcrystalsilicon.
 20. An oxide semiconductor substrate in which the structuralbody according to claim 14 is stacked on an electrically insulatingsubstrate.
 21. A power semiconductor element in which the oxidesemiconductor substrate according to claim 18 is used.
 22. A diodeelement in which the oxide semiconductor substrate according to claim 18is used.
 23. A schottky barrier diode element in which the oxidesemiconductor substrate according to claim 18 is used.
 24. The schottkybarrier diode element according to claim 23, wherein the metal thin filmserves as a schottky electrode layer.
 25. A structural body comprisingan oxide semiconductor layer and a metal thin film, wherein the oxidesemiconductor layer comprises polycrystalline and/or amorphous oxidesemiconductor having a band gap of 3.0 eV or more and 5.6 eV or less;the metal thin film has a work function of 4.7 eV or more and the metalthin film comprises Au, Fe, Ir, Nb, Ni, Pd, Pt, Re or Ru; and thestructural body comprises a region where the oxide semiconductor layerelectrically contacts the metal thin film.
 26. The structural bodyaccording to claim 25, wherein the oxide semiconductor comprises In as amain component.
 27. The structural body according to claim 25, whereinthe oxide semiconductor is crystalline and comprises at least oneelement selected from Al, Si, Ce, Ga, Hf, Zr, Sm, Zn and Sn, and if atleast one element selected from Al, Si, Ce, Ga, Hf, Zr and Sm iscontained, the content thereof is 3 at % or more and 30 at % or lessrelative to the total metal elements, if Zn is contained, the contentthereof is 5 at % or more and 40 at % or less relative to the totalmetal elements, and if Sn is contained, the content thereof is 500 ppmat % or more and 3 at % or less relative to the total metal elements.28. The structural body according to claim 25, wherein the oxidesemiconductor has a carrier concentration at room temperature of 1×10¹⁴cm⁻³ or more and 1×10¹⁷ cm⁻³ or less.
 29. The structural body accordingto claim 25, wherein the film thickness of the oxide semiconductor layeris 50 nm to 20 μm.
 30. An oxide semiconductor substrate in which thestructural body according to claim 25 is stacked on a conductivesubstrate.
 31. The oxide semiconductor substrate according to claim 30,wherein the conductive substrate is composed of one or more selectedfrom monocrystalline silicone, polycrystalline silicon and microcrystalsilicon.
 32. An oxide semiconductor substrate in which the structuralbody according to claim 25 is stacked on an electrically insulatingsubstrate.
 33. A power semiconductor element in which the oxidesemiconductor substrate according to claim 30 is used.
 34. A diodeelement in which the oxide semiconductor substrate according to claim 30is used.
 35. A schottky barrier diode element in which the oxidesemiconductor substrate according to claim 30 is used.
 36. The schottkybarrier diode element according to claim 35, wherein the metal thin filmserves as a schottky electrode layer.